You've all gotten away from the fact that w/o flotation you're screwed sooner. Also, the difference between a PFD and lifejacket is that a PFD will float you, but not necessarily face up whereas a life jacket will float you face up, even unconscious.
As a devout believer that immersion is the greatest enemy to paddlers of all stripes, I am relentless in all of my classes to dress for the water as no one really plans to capsize. In fact, I pointed it out to some renters the other day and I was informed that it was OK, they knew what they were doing. They were experienced sea kayakers...in their wellingtons and rain gear.